The present invention relates to tintable, radiation-curable coating compositions. More particularly, the coating compositions of the present invention form transparent, abrasion-resistant coatings upon exposure to high intensity irradiation that absorb a desired amount of colored dye when immersed in a dye bath for a sufficient period of time.
In recent years, synthetic polymeric materials have been utilized in a wide variety of applications. In particular, the substitution of glass glazing with transparent materials which do not shatter, or are more resistant to shattering than glass, has become widespread. For example, transparent polymeric materials, such as polycarbonates, acrylics, and similar plastics, are commonly used as windows in public buildings. Likewise, transparent polycarbonates and acrylics are used in glazing for automobiles, buses, aircraft and other public transportation vehicles. Lenses for eyeglasses and optical instruments also employ shatter-resistant transparent polymeric materials. In addition to their greater resistance to shattering, these transparent polymeric materials are also lighter in weight than glass which is of particular advantage in the transportation industry where the weight of the vehicle is a major factor in its fuel economy.
Although these transparent polymeric materials may be readily fabricated into a desired shape, unfortunately they have relatively low abrasion resistance. Thus, a serious drawback of these materials is the ease with which they are marred and scratched as a result of normal, everyday contact with abrasives, such as dust, cleaning materials, and ordinary weathering. Continued scratching and marring results in impaired visibility and poor aesthetics, and oftentimes requires replacement of the transparent polymeric material. In addition, many such materials do not absorb significant amounts of a colored dye, and therefore cannot be satisfactorily tinted.
It is known to coat the surface of such transparent polymeric materials with a transparent, abrasion-resistant coating to improve their abrasion resistance. Known abrasion-resistant coatings, also referred to as "hard coatings," include coatings formed from silica-containing mixtures, such as colloidal silica or silica gel, and hydrolyzable silanes in a hydrolysis medium, such as alcohol or water. See, for example, U.S. Pat. Nos. 3,708,225; 3,986,997; and 3,976,497. However, such coatings often are difficult to apply, and require heat to initiate the cure reaction which must then be maintained for a lengthy period of time until the cure reaction is completed.
Colloidal silica has also been used to improve the abrasion resistance of ultraviolet light-curable coatings as shown in Chung, U.S. Pat. No. 4,348,462. Ultraviolet light is one of the most widely used types of radiation for curing chemical compositions because of its relatively low cost, ease of maintenance, and low potential hazard to industrial users. Rapid photo-induced polymerizations utilizing ultraviolet light instead of thermal energy for curing hard coatings offer substantial economic benefits, and expend considerably less thermal energy than conventional heat cure systems. Also, heat sensitive materials can be safely coated and cured with ultraviolet light without the use of thermal energy which can damage such substrates. In addition, radiation cured coatings can utilize lower amounts of solvents, thereby reducing the necessity for expensive and time consuming pollution abatement procedures.
However, known abrasion-resistant coatings, whether cured by thermal energy or high intensity irradiation, cannot be satisfactorily tinted as they do not absorb or transmit sufficient amounts of a colored dye when immersed in a dye bath within a reasonable period of time. This is a particular disadvantage in connection with the manufacture of coatings for ophthalmic lenses where a tinted coating aids in protecting the eyes from sunlight as well as in satisfying fashion-conscious consumers.